“I go after Streptococcus pneumoniae and many other bacteria causing community-acquired pneumonia with vengeance but lately I have had a hard time keeping up with many gram-negatives, including some E. coli. Who am I?”

Additional hint: “The latest FDA warning against the use of my class of drugs has to do with increased risk of ruptures or tears in the aorta in certain patients, including the elderly and those with hypertension, aortic aneurysm or peripheral vascular disease.” 

Editor’s note: This post is part of the P4P “Talking Therapeutics” series designed to make learning about antibiotics fun. Individual antibiotics give a short description of themselves and you are asked to guess their names. Antimicrobial spectrum, common uses and potential adverse effects follow. Enjoy!

And the answer is…… HERE

Selected antimicrobial spectrum

                Gram-positives: Streptococcus pneumoniae, Staphylococcus aureus                         (some resistance even in MSSA), Enterococcus spp (urine;some resistance)

                Gram-negatives: Enterics (eg, E. coli, Klebsiella spp), Pseudomonas spp,                                 Stenotrophomonas maltophilia, H. influenzae, some ESBLs.

                 AVOID: MRSA, anaerobes

Common clinical uses: community-acquired pneumonia (CAP), healthcare-associated pneumonia (HAP), urinary tract infections (UTIs), legionnaire’s disease, abdominal infection (plus anaerobic coverage)

WATCH OUT! QT prolongation, C. difficile, central nervous system toxicity, seizures, myasthenia gravis, peripheral neuropathy, tendinopathy, drug interactions (eg. warfarin), and most recently aortic aneurysm diagnosis/dissection!

Remember the key features of levofloxacin before you prescribe it!

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Selected references

  1. FDA. FDA warns about increased risk of ruptures or tears in the aorta blood vessel with fluoroquinolone antibiotics in certain patients.  https://www.fda.gov/drugs/drug-safety-and-availability/fda-warns-about-increased-risk-ruptures-or-tears-aorta-blood-vessel-fluoroquinolone-antibiotics. Accessed Nov 26, 2020,.
  2. Marangon FB, Miller D, Muallem MS, et al. Ciprofloxacin and levofloxacin resistance among methicillin-sensitive Staphylococcus aureus isolates from keratitis and conjunctivitis. Am J Ophthal 2004;137:453-58. https://www.ajo.com/article/S0002-9394(03)01287-X/pdf
  3. Yasufuku T, Shigemura K, Shirakawa T, et al. Mechanisms of and risk factors for fluoroquinolone resistance in clinical Enterococcus faecalis from patients with urinary tract infections. J Clin Microbiol 2011;49:3912-16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3209098/
  4.  Rawla P, Helou MLE, Vellipuram AR. Fluoroquinolones and the risk of aortic aneurysm or aortic dissection: A systematic review and meta-analysis. Cardiovasc Hematol Agents Med Chem 2019;17:3-10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6865049/

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis or its affiliate healthcare centers. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

“I go after Streptococcus pneumoniae and many other bacteria causing community-acquired pneumonia with vengeance but lately I have had a hard time keeping up with many gram-negatives, including some E. coli. Who am I?”

Why has my patient with Clostridium difficile diarrhea developed Klebsiella bacteremia?

Although there are many potential sources for Klebsiella sp. bacteremia, C. difficile infection (CDI) itself may be associated with GI translocation of enteric organisms.

A retrospective study of over 1300 patients found an incidence of 1.8% for CDI-associated bacteremia. E. coli, Klebsiella sp. , or Enterococcus sp. accounted for 72% of cases. History of malignancy, neutropenia (at the time of CDAD), and younger age (mean 59 y) were among the risk factors.1 Another study reported over 20 cases of bacteremia caused by C. difficile plus other bacteria often of enteric origin such the aforementioned organisms, Bacteroides sp, Candida sp, and Enterobacter sp.2

CDI is thought to predispose to bacterial translocation through the GI tract by alteration of mucosal indigenous microflora, overgrowth of certain pathogens, and presence of inflammation in the mucosa.3 Interestingly, C. difficile toxin A or B may play an active role in the bacterial adherence and penetration of the intestinal epithelial barrier.4  

Bonus pearl: Did you know that C. difficile may be found in the normal intestinal flora of 3% of healthy adults, 15-30% of hospitalized patients, and up to 50% of neonates? Why neonates seem immune to CDI is another fascinating story!



  1. Censullo A, Grein J, Madhusudhan M, et al. Bacteremia associated with Clostridium difficile colitis: incidence, risk factors, and outcomes. Open Forum Infectious Diseases, Volume 2, Issue suppl_1, 1 December 2015, 943, https://doi.org/10.1093/ofid/ofv133.659 https://academic.oup.com/ofid/article/2/suppl_1/943/2635179
  2. Kazanji N, Gjeorgjievski M, Yadav S, et al. Monomicrobial vs polymicrobial Clostridum difficile bacteremia: A case report and review of the literature. Am J Med 2015;128:e19-e26. https://www.amjmed.com/article/S0002-9343(15)00458-1/abstract
  3. Naaber P, Mikelsaar RH, Salminen S, et al. Bacterial translocation, intestinal microflora and morphological changes of intestinal mucosa in experimental models of Clostridium difficile infection. J Med Microbiol 1998; 47: 591-8. https://www.ncbi.nlm.nih.gov/pubmed/9839563 
  4. Clostridium difficile toxins may augment bacterial penetration of intestinal epithelium. Arch Surg 1999;134: 1235-1242. https://jamanetwork.com/journals/jamasurgery/fullarticle/390434
Why has my patient with Clostridium difficile diarrhea developed Klebsiella bacteremia?

Is iron therapy contraindicated in my patient with active infection?

In the absence of randomized-controlled trials of iron therapy in patients with active infection, the harmful effects of iron therapy (IT) in this setting remains more theoretical than proven. 1,2

Although many pathogens (eg, E. coli, Klebsiella, Salmonella, Yersinia, and Staphylococcus species) depend on iron for their growth2,3, and iron overload states (eg, hemochromatosis) predispose to a variety of infections, studies evaluating the risk of infection with iron therapy have reported conflicting results.1-4 A 2015 systematic review and meta-analysis of 103 trials comparing IV iron therapy  with several other approaches, including oral iron therapy or placebo, found no increased risk of infections with IV iron.5 In contrast, an earlier systematic review and meta-analysis involving fewer number of trials found an increased risk of infections with IV iron. 6

These varied results are perhaps not surprising since the effects of iron therapy on the risk of infection is likely to be context-specific, depending on the patient’s preexisting iron status, exposure to potential infections and co-infection and genetic background. 4 Of interest, mice with sepsis have worse outcomes when treated with IV iron.7

Perhaps the most prudent approach is to hold off on iron therapy until the active infection is controlled, unless the benefits of urgent iron therapy is thought to outweigh its theoretical harmful effects.


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  1. Daoud E, Nakhla E, Sharma R. Is iron therapy for anemia harmful in the setting of infection? Clev Clin J Med 2011;78:168-70. http://www.mdedge.com/ccjm/article/95480/hematology/iron-therapy-anemia-harmful-setting-infection
  2. Hain D, Braun M. IV iron: to give or to hold in the presence of infection in adults undergoing hemodialysis. Nephrology Nursing Journal 2015;42:279-83. https://www.ncbi.nlm.nih.gov/pubmed/26207288
  3. Jonker FAM, van Hensbroek MB. Anaemia, iron deficiency and susceptibility of infections. J Infect 204;69:523-27. https://www.ncbi.nlm.nih.gov/pubmed/28397964
  4. Drakesmith H, Prentice AM. Hepcidin and the iron-infection axis. Science 2012;338:768-72. https://www.ncbi.nlm.nih.gov/pubmed/23139325  
  5. Avni T, Bieber A, Grossman A, et al. The safety of intravenous iron preparations: systematic review and meta-analysis. Mayo Clin Proc 2015;90:12-23. http://www.mayoclinicproceedings.org/article/S0025-6196(14)00883-0/pdf
  6. Litton E, Xiao J, Ho KM. Safety and efficacy of intravenous iron therapy in reducing requirement for allogeneic blood transfusion: systematic review and meta-analysis of randomized clinical trials. BMJ 2013;347:f4822. https://www.ncbi.nlm.nih.gov/pubmed/23950195
  7. Javadi P, Buchman TG, Stromberg PE, et al. High dose exogenous iron following cecal ligation and puncture increases mortality rate in mice and is associated with an increase in gut epithelial and splenic apoptosis. Crit Care Med 2004;32:1178-1185. https://www.ncbi.nlm.nih.gov/pubmed/15190970
Is iron therapy contraindicated in my patient with active infection?

Are two sets of blood cultures adequate for evaluation of bacteremia in my febrile patient?

For great majority of patients, more than 2 sets of blood culture obtained closely apart is not likely to significantly improve the yield of detecting bacteremia. 

Although a 2004 report suggested that 2 sets of blood cultures over 24 h period had a sensitivity of only 80% for bacteremia, several other studies have found much higher sensitivities, ranging from ~90%- 99% 2-3. When broken down by organism, sensitivity of 2 sets of blood cultures may be highest for Staphylococcus aureus (97%), followed by E. coli (91%), and Klebsiella pneumoniae (90%) 2.  The Clinical and Laboratory Standards Institute guidelines recommend paired blood culture sets (each set with 2 bottles, 10 ml of blood in each) to detect about 90-95% of patients with documented bacteremia, and 3 sets for 95-99% detection rate 4.

It seems prudent to strike a balance between drawing more than 2 sets of blood cultures—with its attendant risk of picking up contaminants— and what may be a definite but small incremental increase in the rate of detection of true bacteremia. 

If you are concerned about “continuous” bacteremia (eg, in endocarditis) or a common blood culture contaminant causing true disease (eg, Staphylococcus epidermidis prosthetic valve infection), you may consider a 3rd or 4th set of blood cultures drawn 4-6 hrs after the initial sets.

Whatever you do,  please don’t order only 1 set of blood cultures! Aside from its generally low yield, when positive it may be difficult to distinguish contaminants from true invaders.



  1. Cockerill FR, Reed GS, Hughes JG, et al. Clinical comparison of BACTEC 9240 Plus Aerobic/F resin bottles and the Isolator aerobic cultures. Clin Infect Dis 2004;38:1724-30. https://www.ncbi.nlm.nih.gov/pubmed/9163464
  2. Lee A, Mirrett S, Reller LB, et al. Detection of bloodstream infections in adults: how many cultures are needed? J Clin Microbiol 2007; 45:3546-48. http://jcm.asm.org/content/45/11/3546
  3. Towns ML, Jarvis WR, Hsueh PR. Guidelines on blood cultures. J Microbiol Immunol Infect 2010;43:347-49. https://www.ncbi.nlm.nih.gov/pubmed/20688297
  4. Weinstein MP, Reller LB, Murphy JR, et al. The clinical significance of positive blood cultures: a comprehensive analysis of 500 episodes of bacteremia and fungemia in adults. I. Laboratory and eipidemiologic observations. Rev Infect Dis 1982;5:35-53. https://www.ncbi.nlm.nih.gov/pubmed/6828811
Are two sets of blood cultures adequate for evaluation of bacteremia in my febrile patient?